This invention relates to rotating machinery in general and more particularly to apparatus for turning a shaft in such machinery after it has been at rest for a period of time.
When a piece of heavy rotating machinery such a turbine is shut down and the rotor stands still for a long period of time a certain amount of distortion of the rotor occurs during cooling. If a turbine were immediately started up again in this condition, there could be rubbing and a destriction of the blade gap seals. Because of this, turning gear or jacking gear is normally used with turbines to turn them over before being started up during a warming up process. The same devices are used to periodically rotate the turbine a certain number of degrees during long periods of shut-down to avoid a flat being formed at any one spot on the bearings. A type of device for this purpose in the form of a hydraulic turbine mounted on the shaft is disclosed in German Patent No. 975,676. However, when a turbine rotor or the like has been at standstill for a long period of time there is large breakaway torque required to get the rotor moving. This can be so large as to require the jacking gear, such as a hydraulic turning device, to be made of an uneconomically large size if it is to overcome this torque.
In view of this problem, the need for an apparatus for use with a machine shaft such as a turbine rotor which can be used to easily break it loose after it has been standing still for a long time and furthermore to permit a stepwise turning of the shaft, e.g. the turbine rotor, is evident.